BLOG: Fixational eye movements impaired after concussion
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The oculomotor system serves as a window into brain health and function because so many parts of the brain are involved in planning, coordinating and executing eye movements.
Our group recently conducted a study in which we tracked and evaluated fixational eye movements (FEMs) in patients following a concussion.
When the eye fixates, one might imagine that it is still, but in fact there are constant involuntary movements that help maintain the gaze on a stationary object or location. Many of these movements could be characterized as microsaccades but, because that term is poorly defined, we simply evaluated all the saccades that occurred during simple fixational tasks of staring at the center or the corner of a 5° x 5° dim red square.
We used a tracking scanning laser ophthalmoscope (TSLO) that directly tracks movements of the retina, which is very different from other approaches to eye tracking, most of which rely on external videography. Our TSLO approach had its genesis, ironically, in efforts to “undo” this constant motion of the eye to obtain better images of individual cells in the retina. Software that we use to compensate for FEMs in the context of understanding retinal disease turns out to also have advantages for tracking and measuring what happens to FEMs after concussion.
In the study (Leonard et al.), we found that adolescents and young adults (ages 13-27) who had experienced a concussion within the past 21 days had significantly larger and less well-controlled FEMs (that is, greater fixational saccade amplitude, velocity and acceleration) than control subjects who had not had a recent concussion when fixating on the center of the target. (There were no statistically significant differences when subjects fixated on the corner of the square.) Analysis of FEMs during a third, more active fixation task is ongoing and will be published in a future paper.
This study provides fertile ground for further research into concussion-induced oculomotor dysfunction. In particular, we would like to know how the types of oculomotor deficits we can detect with the TSLO technology correlate with other concussion diagnostics. It will also be important to learn more about the impact of age and mechanism of injury on these subtle FEM changes during recovery.
Retinal eye tracking evaluation of FEMs could provide a quick and objective way to assess ocular dysfunction. Not only could this aid in diagnosing and determining the severity of brain injury, but it could also potentially contribute to our understanding of how neurodegenerative diseases affect the oculomotor system.
Reference:
- Leonard BT, et al. J Vis. 2021;doi:10.1167/jov.21.13.11.
For more information:
Ethan A. Rossi, PhD, is assistant professor of ophthalmology and bioengineering at the University of Pittsburgh School of Medicine. He also serves on the faculty of the university’s Center for Neuroscience. Rossi has a longstanding interest in eye tracking and eye movement. His research has focused on using high-resolution imaging technologies and adaptive optics to probe the limits of human vision in both normal and diseased eyes.
Disclaimer: The views and opinions expressed in this blog are those of the authors and do not necessarily reflect the official policy or position of the Neuro-Optometric Rehabilitation Association unless otherwise noted. This blog is for informational purposes only and is not a substitute for the professional medical advice of a physician. NORA does not recommend or endorse any specific tests, physicians, products or procedures. For more on our website and online content, click here.
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